Video surveillance systems are known wherein video cameras are deployed at remote locations that are desired to be monitored by security personnel. In such systems, images from several cameras are displayed on one or more video monitors at a security console. By having a single person remotely monitoring a large number of locations, a considerable cost advantage can be realized compared to employing several people to be stationed in the locations of interest.
Traditionally, the video cameras employed in such surveillance systems have been somewhat unsophisticated relative to video cameras used in television broadcasting systems or cameras intended for home use. For almost every operational feature that may be incorporated into a video camera, there is a corresponding parameter that must be set and/or adjusted by the user. The need for such adjustments is not an overwhelming problem for the user of a single camera. However, the use of feature-laden cameras in a surveillance system having many cameras requires a significantly greater amount of the user's attention in order to set or maintain adjustments of the multitude of parameters for each camera. Even if each camera were to be initially adjusted according to a set of pre-determined parameters, the required adjustments are likely to change in response to changing camera orientations, changing lighting conditions, or other events within a monitored area. Thus, the user of a surveillance system would be distracted from the task of providing vigilant attention to activities in the monitored areas. For example, simply maintaining and adjusting a plurality of remote video cameras in focus could present a significant distraction to the user.
It would be desirable to provide a multiple-camera surveillance system wherein the cameras are capable of automatically adjusting certain operational parameters, such as the focus setting, of each of the cameras. Additionally, it would be desirable to provide a multiple-camera surveillance system wherein manual adjustments of several camera parameters can be made remotely, stored, and then retrieved in association with the reorientation of the camera.
In particular, it would be desirable to provide such storage and retrieval of parameters in connection with the focus and/or white balance of a color video camera. In order to obtain accurate color images from a video camera, it is necessary to equalize, or balance, the levels of red, green, and blue in a video signal relative to the detected levels of such colors, in accordance with the spectrum of the light in the observed area. Sunlight, for example, has a spectrum that approximates a 5,500K blackbody, hence the spectrum of reflected light from a white object will exhibit a peak in the green region. The spectra of incandescent lamps can be approximated by blackbody spectra at various temperatures depending upon the type of lamp. Still other sources of light, such as metal vapor lamps or fluorescent tubes, exhibit prominent peaks at various locations within the spectrum. A figure of merit that is used to characterize the spectrum of a light source is referred to as the color temperature of the light source. In the field of photography, colored filters are used to compensate, or equalize, the response of color film to account for various color temperatures. In electronic imaging systems, it is common to provide a variable gain device, known as a white balance system, to allow the user to equalize the response of an electronic imaging device in accordance with the prevailing color temperature.
In some applications the remote surveillance unit is employed in a location having different areas each of which can be characterized by a color temperature. For example, one area within a room may have incandescent lighting, while another area of the room may have fluorescent lighting, or a window providing sunlight. Automatic white balance systems are known wherein the levels of compensation applied to the color components of a video image are continuously adjusted in response to the measured color content of the image. Such white balance systems each rely upon a statistical assumption in regard to what the color content of a balanced image should be. If, for example, there is relatively little white actually in an area being viewed, an automatic white balance system may incorrectly distort the colors in the video image. Additionally, the continuous color adjustment provided by automatic white balance often causes color instability within the video image, particularly if there are fluctuations in the color content of the area as may be caused by movement of the camera or objects in the image.
White balance settings can be adjusted manually by the camera operator, but manual adjustment would be a distraction to the user of a video surveillance system, especially a system wherein a plurality of remotely positionable cameras are employed. It would be desirable to provide a video surveillance system in which predefined white balance settings can be stored in association with corresponding areas that may be viewed by each camera. Then, these settings can be automatically retrieved, and applied to the detected video image whenever the camera is reoriented to view one of the selected areas, which may have a different color temperature than a previously viewed area.
In some applications, it is desirable to provide the surveillance system user with the ability to set or adjust the shutter speed of a remote surveillance camera. For example, in a dimly illuminated area, a low shutter speed is generally desirable. Whereas, in a brightly illuminated area, a relatively high shutter speed is generally desirable. Additionally, a surveillance camera may be employed in an area where it is desirable to obtain a clear image of moving objects, e.g., vehicles, that may pass through the area. It would be desirable to provide the user with the ability to set or adjust the shutter speed of a remote surveillance camera depending upon the circumstances presented in the monitored area.